Actuator, optical scanner and image forming apparatus

ABSTRACT

An actuator includes: a first vibrating system having a frame-like driving member and a pair of first axis members holding the driving member from both sides so that the driving member is rotatable about an X axis; a second vibrating system having a movable plate provided inside the driving member and a pair of second axis members holding the movable plate on the driving members from both sides so that the movable plate is rotatable about a Y axis orthogonal to the X axis; a driving unit including a permanent magnet provided on the driving member, a coil provided to oppose the permanent magnet and a voltage applying unit applying voltage to the coil; and a spacer sandwiched between the driving member and the permanent magnet so as to form space preventing intervention by the movable plate.

CROSS REFERENCE TO RELATED APPLICATIONS

This application is a continuation application of U.S. Ser. No.12/030,383 filed Feb. 13, 2008, claiming priority to Japanese PatentApplication No. 2007-057816 filed Mar. 7, 2007, all of which are herebyexpressly incorporated by reference in their entirety.

BACKGROUND OF THE INVENTION

1. Technical Field

The present invention relates to an actuator, an optical scanner and animage forming apparatus.

2. Related Art

As an optical scanner used for drawing by utilizing optical scanning ina printer or the like, there is known one performing two-dimensionalscanning (see, for example JP-A-08-322227).

The optical scanner disclosed in JP-A-08-322227 has a scanner main bodyincluding a frame-like outer movable plate, a pairs of first torsionbars axially supporting the outer movable plate so that the outermovable plate is swingably supported (rotatable) about an X axis, aninner movable plate provided inside the outer movable plate, a pair ofsecond torsion bars axially supporting the inner movable plate so thatthe inner movable plate is swingable about a Y axis orthogonal to the Xaxis, a pair of driving coils respectively provided in the outer movableplate and the inner movable plate, and a pair of permanent magnetsprovided so as to oppose each other through the intermediation of thescanner main body.

In such the optical scanner, however, the permanent magnets are providedso as to be opposite to each other through the intermediation of thescanner main body, so miniaturization of the light scanner can hardly beachieved. Further, the outer movable plate and the inner movable plateare respectively provided with one driving coil, so it is difficult toachieve cost reduction.

SUMMARY

An advantage of the present invention is to provide an actuator, anoptical scanner and an image forming apparatus, according to which lowcost and miniaturization can be achieved while the movable plate canrotate about an X axis and a Y axis orthogonal to the X axis.

An actuator according to one aspect of the invention includes: a firstvibrating system having a frame-like driving member and a pair of firstaxis members holding the driving member from both sides so that thedriving member is rotatable about an X axis; a second vibrating systemhaving a movable plate provided inside the driving member and a pair ofsecond axis members holding the movable plate on the driving membersfrom both sides so that the movable plate is rotatable about a Y axisorthogonal to the X axis; a driving unit including a permanent magnetprovided on the driving member, a coil provided to oppose the permanentmagnet and a voltage applying unit applying voltage to the coil; and aspacer sandwiched between the driving member and the permanent magnet soas to form space preventing intervention by the movable plate. Thepermanent magnet is provided such that a line segment connecting bothpoles of the permanent magnet inclines, in a plan view of the movableplate, with respect to the X axis and the Y axis. The voltage applyingunit includes a voltage generating portion generating a firstalternating voltage and a second alternating voltage having differentfrequencies and a voltage superimposing portion superimposing the firstvoltage and the second voltage. The voltage superimposed at the voltagesuperimposing portion is applied to the coil so that the movable platerotates about the X axis with a frequency of the first voltage and aboutthe Y axis with a frequency of the second voltage.

As a result, the actuator capable of achieving reduction in cost andminiaturization while the movable plate can rotate about the X axis andthe Y axis.

In this case, it is preferable that the spacer be integrally formed withthe driving member.

Accordingly, the fabrication of the actuator can be simplified.

In this case, it is preferable that the driving member be formed fromone Si layer of a SOI substrate and the spacer be formed from at least aSiO₂ layer. The SOI substrate has the SiO₂ layer, the one Si layer andthe other Si layer.

As a result, it becomes possible to more reliably form the spacer on thedriving member in a desired place.

In this case, it is preferable that the spacer be provided as one pair.

As a result, the pair of spacers can be used as a positioning portionfor the permanent magnet.

In this case, it is preferable that the frequency of the second voltagebe the same as a resonance frequency of the second vibrating system andthe frequency of the first voltage be different from a resonancefrequency of the first vibrating system.

As a result, it becomes possible to let the movable plate highlysmoothly rotate about the X axis and the Y axis.

In this case, it is preferable that the frequency of the second voltagebe larger than the frequency of the first voltage.

As a result, it becomes possible to let the movable plate rotate morereliably and smoothly about the X axis with the frequency of the firstvoltage and also about the Y axis with the frequency of the secondvoltage.

In this case, it is preferable that the permanent magnet have alongitudinal shape and being provided along a line segment passingthrough an intersecting point of the X axis and the Y axis and incliningwith respect to one of the X axis and the Y axis at an angle of 30° to60°

By this, it becomes possible to let the movable plate rotate highlysmoothly about the X axis and the Y axis.

In this case, it is preferable that the coil be provided directly underthe permanent magnet.

As a result, it becomes possible to let the magnetic field generatedfrom the coil efficiently effect on the permanent magnet. Accordingly,power saving and miniaturization of the actuator can be achieved.

In this case, it is preferable that the coil be, seen in a plan view ofthe movable plate, formed so as to surround outer periphery of thedriving member.

As a result, the distance between the coil and the permanent magnet canbecome highly small, thereby making it possible to let the magneticfield generated from the coil efficiently effect on the permanentmagnet. That is to say, power saving and miniaturization of the actuatorcan be achieved while the rotation angle of the movable plate can beenlarged.

In this case, it is preferable that the movable plate include a lightreflecting portion having light reflective properties on one surfacethereof opposite from the other surface adjacent to the permanentmagnet.

As a result, the actuator according to the invention can be used as anoptical device to be provided in an image forming apparatus such as alaser printer, a barcode reader, a confocal scanning laser microscope oran imaging display.

According to a second aspect of the invention, an optical scannerincludes a first vibrating system having a frame-like driving member anda pair of first axis members holding the driving member from both sidesso that the driving member is rotatable about an X axis; a secondvibrating system having a movable plate provided inside the drivingmember and a pair of second axis members holding the movable plate onthe driving members from both sides so that the movable plate isrotatable about a Y axis orthogonal to the X axis; a driving unitincluding a permanent magnet provided on the driving member, a coilprovided to oppose the permanent magnet and a voltage applying unitapplying voltage to the coil; and a spacer sandwiched between thedriving member and the permanent magnet so as to form space preventingintervention by the movable plate. The permanent magnet is provided suchthat a line segment connecting both poles of the permanent magnetinclines, in a plan view of the movable plate, with respect to the Xaxis and the Y axis. The voltage applying unit includes a voltagegenerating portion generating a first alternating voltage and a secondalternating voltage having different frequencies and a voltagesuperimposing portion superimposing the first voltage and the secondvoltage. The voltage superimposed at the voltage superimposing portionis applied to the coil so that the movable plate rotates about the Xaxis with a frequency of the first voltage and about the Y axis with afrequency of the second voltage so as to perform a two-dimensionalscanning of light reflected at the light reflecting portion.

Accordingly, it becomes possible to provide an optical scanner accordingto which low cost and miniaturization can be achieved while the movableplate can rotate about two axes intersecting each other (the X axis andthe Y axis), thereby performing two-dimensional scanning of light.

According to a third aspect of the invention, an image forming apparatusincludes an optical scanner including: a first vibrating system having aframe-like driving member and a pair of first axis members holding thedriving member from both sides so that the driving member is rotatableabout an X axis; a second vibrating system having a movable plateprovided inside the driving member and a pair of second axis membersholding the movable plate on the driving members from both sides so thatthe movable plate is rotatable about a Y axis orthogonal to the X axis;a driving unit including a permanent magnet provided on the drivingmember, a coil provided to oppose the permanent magnet and a voltageapplying unit applying voltage to the coil; and a spacer sandwichedbetween the driving member and the permanent magnet so as to form spacepreventing intervention by the movable plate. In the scanner, thepermanent magnet is provided such that a line segment connecting bothpoles of the permanent magnet inclines, in a plan view of the movableplate, with respect to the X axis and the Y axis, and the voltageapplying unit includes a voltage generating portion generating a firstalternating voltage and a second alternating voltage having differentfrequencies and a voltage superimposing portion superimposing the firstvoltage and the second voltage. The voltage superimposed at the voltagesuperimposing portion is applied to the coil so that the movable platerotates about the X axis with a frequency of the first voltage and aboutthe Y axis with a frequency of the second voltage so as to perform atwo-dimensional scanning of light reflected at the light reflectingportion.

Accordingly, it becomes possible to provide an image forming apparatusprovided with an optical scanner according to which low cost andminiaturization can be achieved while the movable plate can rotate abouttwo axes intersecting each other (the X axis and the Y axis), therebyperforming a two-dimensional scanning of light.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will be described with reference to the accompanyingdrawings, wherein like numbers reference like elements.

FIG. 1 is a plan view showing a preferable embodiment of an actuatoraccording to the invention.

FIG. 2 is a sectional view taken along with the line A-A of FIG. 1.

FIG. 3 is a block diagram showing a voltage applying unit of a drivingunit included in the actuator shown in FIG. 1.

FIG. 4A is a view showing an example of a first voltage generatingportion shown in FIG. 3.

FIG. 4B is a view showing an example of a second voltage generatingportion shown in FIG. 3.

FIG. 5A is a view for illustrating a method for manufacturing theactuator shown in FIG. 1.

FIG. 5B is a view for illustrating a method for manufacturing theactuator shown in FIG. 1.

FIG. 5C is a view for illustrating a method for manufacturing theactuator shown in FIG. 1.

FIG. 5D is a view for illustrating a method for manufacturing theactuator shown in FIG. 1.

FIG. 5E is a view for illustrating a method for manufacturing theactuator shown in FIG. 1.

FIG. 5F is a view for illustrating a method for manufacturing theactuator shown in FIG. 1.

FIG. 5G is a view for illustrating a method for manufacturing theactuator shown in FIG. 1.

FIG. 5H is a view for illustrating a method for manufacturing theactuator shown in FIG. 1.

FIG. 6 is a schematic view showing an image forming apparatus accordingto the invention.

DESCRIPTION OF EXEMPLARY EMBODIMENTS

Hereinafter, preferable embodiments of an actuator, an optical scannerand an image forming apparatus according to the present invention willbe described with reference to the attached drawings.

FIG. 1 is a plan view showing a preferable embodiment of the actuatoraccording to the invention. FIG. 2 is a sectional view along with theline A-A of FIG. 1. FIG. 3 is a block diagram showing a driving unitincluded in the actuator shown in FIG. 1. FIG. 4A and FIG. 4Brespectively show examples of a generated voltage at a first voltagegenerating portion and a second voltage generating portion. Note thathereinafter for the sake of convenience of explanation the front side ofFIG. 1 is called upper side, the rear side thereof is called bottomside, the right side thereof is called right side and the left sidethereof is called left side. Further, the upper side of FIG. 2 is calledupper side, the bottom side thereof is called bottom side, the rightside thereof is called right side and the left side thereof is calledleft side.

As shown in FIG. 1, the actuator 1 includes a base body 2 having a firstvibrating system 21 and a second vibrating system 22. As shown in FIG.2, the actuator 1 includes a supporting substrate 3 that supports thebase body 2, an opposite substrate 5 opposite to the base substrate 2through the intermediation of the supporting substrate 3, driving unitsthat respectively drive the first vibrating system 21 and the secondvibrating system 22, and spacers 81, 82 that form space 83.

As shown in FIG. 1, the base body 2 includes a frame-like supportingportion 23, the first vibrating system 21 supported by the supportingportion 23, and the second vibrating system 22 supported by the firstvibrating system 21.

The first vibrating system 21 includes a frame-like driving member 211provided inside the supporting portion 23 and a pair of first shaftmembers 212, 213 that support the driving member 211 from both sides onthe supporting portion 23. Further, the second vibrating system 22includes a movable plate 22 provided inside the frame-like drivingmember 211 and a pair of second axis members 222, 223 that support themovable plate 221 from both sides on the driving member 211.

In other words, the base body 2 includes the movable plate 221, the pairof second axis members 222, 223, the driving member 211, the pair offirst axis members 212, 213 and the supporting portion 23.

The driving member 211 has annular shape seen in a plan view of FIG. 1(i.e., seen in a plan view of the movable plate 221). However, it shouldnot be construed restrictively. The shape of the driving member 211 isnot limited thereto as long as it is frame-like shape. Provided on thebottom side of the driving member 211 is a permanent magnet (describedlater) through the intermediation of spacers 81, 82. The driving member211 thus described is supported by the pair of first axis members 212,213 from the both sides on the supporting portion 23.

The first axis members 212, 213 each have longitudinal shape and areelastically deformable. Each of the first axis members 212, 213 connectsthe driving member 211 to the supporting member 23 so that the drivingmember 211 is rotatable with respect to the supporting member 23. Thefirst axis members 212, 213 thus described are provided so as to becoaxial to each other and constructed such that the driving member 211rotates about the axis shared by the first axis members (hereinaftercalled rotation center axis X) with respect to the supporting member 23.

The movable plate 221 provided inside the driving member 211 has aring-like shape seen in plan view of FIG. 1. However, it should not beconstrued restrictively. The shape of the movable plate 221 is notlimited thereto as long as it can be provided inside the driving member211. Provided on the upper surface (the surface far from the oppositesubstrate 5) is a light reflecting portion 221 a that islight-reflective. The movable plate 221 thus described is supported bythe pair of second axis members 222, 223 from the both sides on thedriving members 211.

The second axis members 222, 223 each have longitudinal shape and areelastically deformable. Each of the second axis members 222, 223connects the movable plate 221 to the driving member 211 so that themovable plate 221 is rotatable with respect to the driving member 211.The second axis members 222, 223 thus described are provided so as to becoaxial to each other and constructed such that the movable plate 221rotates about the axis shared by the second axis members (hereinaftercalled rotation center axis Y) with respect to the driving member 211.

As shown in FIG. 1, the rotation center axis X and the rotation centeraxis Y intersect each other. In other words, the angle made by therotation center axis X and the rotation center axis Y is 90°. Further,the center of the driving member 211 and the center of the movable plate221 are both located at the intersecting point of the rotation centeraxis X and the rotation center axis Y, seen in a plan view of FIG. 1.

The main material of the base body 2 thus described is, for example,silicon so that the movable plate 221, the second axis members 222, 223,the driving member 211, the first axis members 212, 213 and thesupporting portion 23 are integrally formed. As thus silicon is used asthe main material, it becomes possible to achieve excellent rotatabilityand high endurance. Furthermore, it becomes possible to perform fineprocessing (working), thereby making it possible to achieveminiaturization of the actuator 1.

Note that the base body 2 may be formed such that the movable plate 221,the second axis members 222, 223, the driving member 211, the first axismembers 212, 213 and the supporting member 23 are formed from asubstrate having a laminated structure such as SOI substrate. In thiscase, the movable plate 221, the second axis members 222, 223, thedriving member 211, the first axis members 212, 213 and the supportingmember 23 are preferably formed by one layer of a substrate of alaminated structure so that those are formed integrally.

The base body 2 thus described is supported by the supporting substrate3. The supporting substrate 3 is, as such, made mainly from glass orsilicon, for example. The supporting substrate 3 has substantially thesame shape as the supporting portion 23, seen in a plan view of themovable plate 221. However, it should not be construed restrictively.The shape of the supporting substrate 3 is not limited thereto as longas the supporting substrate can support the base body 2. Depending onthe shape etc. of the supporting portion 23, it is also possible to omitthe supporting substrate 3. The bonding technique for bonding thesupporting substrate 3 thus described and the base body 2 is not limitedto any particular technique. For example, it is possible to performbonding by using adhesive or by using anodic bonding. Further, a SiO₂layer made mainly from SiO₂, for example, may be sandwiched between thebase body 2 and the supporting body 3.

As shown in FIG. 2, the plate-like opposite substrate 5 is provided soas to be opposite to the base body 2 via the supporting substrate 3. Theopposite substrate 5 thus described is made mainly from, for example,glass or silicon.

Provided on the upper surface of the opposite substrate 5 is a coil 62that is used for generating magnetic field on the permanent magnet 61.As shown in FIG. 2, the coil 62 is electrically connected to a voltageapplying unit 63. A driving unit 6 is made up of such the permanentmagnet 61, the coil 62 and the voltage applying unit 63.

As shown in FIG. 1 and FIG. 2, the permanent magnet 61 has alongitudinal shape. The permanent magnet 61 is bonded to the bottomsurface (the surface opposite to the opposite substrate 5) of thedriving member 211 through the intermediation of the spacers 81, 82. Inother words, the permanent magnet 61 is provided so as to be opposite tothe surface far from the light reflecting portion 221 a of the movableplate 221. By this, the interference of light scanning at the lightreflecting portion 221 a due to the permanent magnet 61 can be reliablyprevented.

The bonding technique of the spacers 81, 82 and the permanent magnet 61is not limited to particular technique. It is also possible to bond thespacers 81, 82 and the permanent magnet 61 by using adhesivetherebetween.

The permanent magnet 61 extends through the intersecting point of therotation center axis X and the rotation center axis Y (hereinafter thisintersecting point is also called intersecting point G), seen in planview of FIG. 1, and is provided along a line segment (hereinafter thisline segment is also called line segment J) inclining with respect tonot only the rotation center axis X but also the rotation center axis Y.

The permanent magnet 61 thus described has with respect to theintersecting point G in the longitudinal direction south pole at oneside and north pole at the other side. That is to say, the line segment(i.e. the line segment J) connecting the south pole and the north poleof the permanent magnet 61 inclines with respect to both of the rotationcenter axis X and the rotation center axis Y. Further, the permanentmagnet 61 shown in FIG. 2 has its south pole on the left-hand side inthe longitudinal direction and its north pole on the right-hand side forthe sake of convenience of explanation.

The inclination angle θ of such the line segment J with respect to therotation center axis X is preferably 30° to 60°, more preferably 40° to50°, and yet preferably about 45°. By thus providing the permanentmagnet 61, it becomes possible to let the movable plate 221 rotateextremely smoothly about the rotation center axis X and the rotationcenter axis Y. On the other hand, when the inclination angle θ is underthe above-mentioned lower limit, there may arise the problem in that themovable plate 221 can not rotate smoothly about the rotation center axisX depending on the strength of the voltage applied to the coil 62 etc.Meanwhile, when the inclination angle θ is above the above-mentionedupper limit, there may arise the problem in that the movable plate 221can not rotate smoothly about the rotation center axis Y depending onthe strength of the voltage applied to the coil 62 etc.

According to this embodiment of the invention, the line segment Jinclines with respect to the rotation center axis X and the rotationcenter axis Y at an angle of 45° in either case.

The permanent magnet 61 is not limited to the above-mentioned one. It isalso possible to preferably use, for example, hard magnetic materialmagnetized such as neodymium magnet, ferrite magnet, samarium-cobaltmagnet, alnico magnet and bond magnet.

The hard magnetic material already magnetized (i.e. permanent magnet)may be provided on the driving member 211 through the intermediation ofthe spacers 81, 82 so that they can be used as the permanent magnet 61.Further, the hard magnetic material may be provided on the drivingmember 211 through the intermediation of the spacers 81, 82 and thenmagnetized to be used as the permanent magnet 61.

A pair of the spacers 81, 82 is sandwiched between the permanent magnet61 thus described and the driving member 211. The spacers 81, 82 formspace 83 that enables prevention of the intervention between thepermanent magnet 61 and the movable plate 221. By providing such thespace 83, it is possible to let the movable plate 221 rotate highlysmoothly about the rotation center axis Y. Further, since the use of thespacers 81, 82 makes it possible to easily form the space 83, thefabrication of the actuator 1 can be easily carried out.

Moreover, the pair of spacers 81, 82 can be used as positioning portionsthat makes it possible to determine the fixed position of the permanentmagnet 61 on the driving member 211. In other words, the spacers 81, 82can also be used as markings for arrangement of the permanent magnet 61.Therefore, it is possible to position the permanent magnet 61 moreaccurately in a desired place.

In particular, in the case of the actuator 1, the length of the spacer81 in the width direction (i.e. direction orthogonal to the line segmentJ in a plan view of FIG. 1) of the permanent magnet 61 is substantiallythe same as the width of the permanent magnet 61 and the length of thespacer 82 in the width direction of the permanent magnet 61 issubstantially the same as the width of the permanent magnet 61.Therefore, the spacers 81, 82 can be highly effectively used aspositioning members for the permanent magnet 61.

The material of such the spacers 81, 82 is not limited to particularone. It is possible to use for this purpose, for example, glass,silicon, ceramics, various metal material such as Li, Be, B, Na, Mg, Al,K, Ca, Sc, V, Cr, Mn, Fe, Co, Ni, Cu, Zn, Ga, Rb, Sr, Y, Zr, Nb, Mo, Cd,In, Sn, Sb, Cs, Ba, La, Hf, Ta, W, Tl, Pb, Bi, Ce, Pr, Nd, Pm, Sm, Eu,Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu, Ag, Au, Pt or Pd, various thermo-settingresins, various thermoplastic resins etc.

According to this embodiment of the invention, as shown in FIG. 2, thespacer 81 includes a base portion 811 mainly formed by SiO₂ and a tipportion 812 mainly formed by silicon. Likewise, the spacer 82 includes abase portion 821 mainly formed by SiO₂ and a tip portion 822 mainlyformed by silicon. By thus forming the spacers 81, 82, it becomespossible to highly easily form the spacers 81, 82 and the driving member211 integrally.

To be more specific, according to a method for manufacturing theactuator 1 described later, the base body 2 is formed from a Si layer onone side of the SOI substrate, the base portions 811, 812 are formedfrom a SiO₂ layer, and the tip portions 812, 822 are formed from a Silayer on the other side of the SOI substrate, thereby making it possibleto form the spacers 81, 82 and the driving member 211 integrally. Itshould be noted, however, that the spacers 81, 82 may also be formedsolely from, for example, a SiO₂ layer of the SOI substrate.

Furthermore, by thus forming the spacers 81, 82 and the driving member211 integrally, the spacers 81, 82 can be more accurately positioned onthe driving member 211 in a desired place.

Provided directly under the permanent magnet 61 provided on the drivingmember 211 through the intermediation of the spacers 81, 82 describedabove is the coil 62. In other words, the coil 62 is provided so as tooppose the respective bottom surfaces of the movable plate 221 and thedriving member 211. By this, the magnetic field generated from the coil62 can efficiently effect the permanent magnet 61, thereby making itpossible to achieve power saving and miniaturization of the actuator 1.

As shown in FIG. 1, the coil 62 is formed, seen in a plan view of FIG.1, so as to surround the outer periphery of the driving member 211. Bythus providing the coil 62, it becomes possible to reliably prevent thedriving member 211 and the coil 62 from coming into contact with eachother when the actuator 1 is driven. Accordingly, it becomes possible tomake the magnetic field generated from the coil 62 effect efficiently onthe permanent magnet 61. That is to say, power saving andminiaturization of the actuator 1 can be achieved while the rotationangle (amplitude) of the movable plate 221 can be enlarged.

Such the coil 62 is electrically connected to the voltage applying unit63. As the voltage applying unit 63 applies voltage to the coil 62, thecoil 62 generates magnetic fields having magnetic flux in the axisdirection orthogonal to both of the rotation center axis X and therotation center axis Y. It should be noted that such the coil 62 maywind around a core.

As shown in FIG. 3, the voltage applying unit 63 includes a firstvoltage generating portion 631 that generates first voltage V1 forrotation of the movable plate 221 about the rotation center axis X, asecond voltage generating portion 632 that generates second voltage V2for rotation of the movable plate 221 about the rotation center axis Y,and a voltage superimposing portion 633 that superimposes the firstvoltage V1 and the second voltage V2 and applies the resulting voltageto the coil 62.

As shown in FIG. 4A, the first voltage generating portion 631 is usedfor generating the first voltage V1 (voltage for vertical scanning)changing periodically in a period T1.

The first voltage V1 has a sawtooth-like waveform. Therefore, theactuator 1 can effectively perform vertical scanning of light(sub-scanning). Note that the waveform of the first voltage V1 is notlimited thereto. In this case, the frequency of the first voltage V1(1/T1) is not limited as long as it is suitable for vertical scanningbut is preferably 30 to 80 Hz (about 60 Hz).

According to this embodiment of the invention, the frequency of thefirst voltage V1 is adjusted so as to be different from a torsionalresonance frequency of the first vibrating system 21 including thedriving member 211 and the pair of first axis members 212, 213.

On the other hand, as shown in FIG. 4B, the second voltage generatingportion 632 generates second voltage V2 (voltage for horizontalscanning) changing periodically in a period T2, which is different fromthe period T1.

The second voltage V2 has a sinusoidal waveform. Therefore, the actuator1 can effectively perform main scanning of light. Note that the waveformof the second voltage V2 is not limited thereto.

The frequency of such the second voltage V2 is preferably larger thanthat of the first voltage V1. In other words, the period T2 ispreferably shorter than the period T1. By this, it becomes possible tolet the movable plate 221 more reliably and smoothly about the rotationcenter axis X with the frequency of the first voltage V1 and also aboutthe rotation center axis Y with the frequency of the second voltage V2.

Further, the frequency of the second voltage V2 is not limited as longas it is different from the frequency of the first voltage V1 andsuitable for horizontal scanning. However, the frequency of the secondvoltage V2 is preferably 10 to 40 Hz. By thus making the second voltageV2 be 10 to 40 Hz and the first voltage V1 be 60 Hz, as described above,the movable plate 221 can rotate about two axes (rotation center axis Xand rotation center axis Y) intersecting each other with a frequencysuitable for drawing on a display. However, the combination of thefrequencies of the first voltage V1 and the second voltage V2 is notlimited as long as the movable plate 221 can rotate about the rotationcenter axis X and the rotation center axis Y.

According to this embodiment of the invention, the frequency of thesecond voltage V2 is set so as to be the same as a torsional resonancefrequency of the second vibrating system 22 including the movable plate221 and the pair of second axis members 222, 223. In other words, thesecond vibrating system 22 is designed (fabricated) such that thetorsional resonance frequency described above becomes suitable forhorizontal scanning. Accordingly, it becomes possible to make therotation angle of the movable plate 221 with respect to the rotationcenter axis Y larger.

Further, it is preferable that f₁ and f₂ satisfy the expression f₂>f₁,and it is more preferable that f₁ and f₂ satisfy the expression f₂>f₁,wherein the resonance frequency of the first vibrating system 21 is f₁[Hz] and the resonance frequency of the second vibrating system 22 is f₂[Hz]. By this, it becomes possible to let the movable plate 221 rotateabout the rotation center axis X at the frequency of the first voltageV1 and also about the rotation center axis Y at the frequency of thesecond voltage V2.

The first voltage generating portion 631 and the second voltagegenerating portion 632 are each connected to a control portion 7 anddriven based on signals from the control portion 7. The voltagesuperimposing portion 633 is connected to such the first voltagegenerating portion 631 and the second voltage generating portion 632.

The voltage superimposing portion 633 includes an superimposer 633 a tobe used for applying voltage to the coil 62. The superimposer 633 areceives the first voltage V1 from the first voltage generating portion631 and the second voltage V2 from the second voltage generating portion632 and then superimposes those voltages to apply the resulting voltageto the coil 62.

The actuator 1 thus descried is driven as follows. It should be notedthat according to this embodiment, the frequency of the first voltage V1is set to be different from the torsional resonance frequency of thefirst voltage system 21 and the frequency of the second voltage V2 issame as the torsional resonance frequency of the second vibrating system22 and larger than the frequency of the first voltage V1 (For instance,the frequency of the first voltage V1 is 60 Hz and the frequency of thesecond voltage V2 is 15 Hz).

For example, the first voltage V1 shown in FIG. 4A and the secondvoltage V2 shown in FIG. 4B are superimposed at the voltagesuperimposing portion 633 and the resulting superimposed voltage isapplied to the coil 62.

Then, the magnetic field (this magnetic field is to be called magneticfield A1) that tends to draw the area around the spacer 81 of thedriving member 211 toward the coil 62 by using the first voltage V1 andseparate the area around the spacer 82 of the driving member 211 fromthe coil 62 and the magnetic field (this magnetic field is to be calledmagnetic field A2) that tends to separate the area around the spacer 81of the driving member 211 from the coil 62 and draw the area around thespacer 82 of the driving member 211 toward the coil 62 are alternatelyswitched.

In this case, seen in a plan view of FIG. 1, the spacer 81 is positionedon one side with respect to the rotation center axis X of the drivingmember 211 and the spacer 82 on the other side. In other words, thespacers 81, 82 are arranged so as to sandwich the rotation center axis Xseen in a plan view of FIG. 1. Therefore, as the magnetic filed A1 andthe magnetic field A2 described above are switched alternately, thefirst axis members 212, 213 are deformed to be twisted while the drivingmember 211 and the movable plate 221 rotate together about the rotationcenter axis X with the frequency of the first voltage V1.

Note that the frequency of the first voltage V1 is set to be extremelylower than the frequency of the second voltage V2. Further, theresonance frequency of the first vibrating system 21 is set to be lowerthan that of the second vibrating system 22 (For instance, less thantenth part of the resonance frequency of the second vibrating system22). In other words, the first vibrating system 21 is designed to be aptto vibrate than the second vibrating system 22. Therefore, the firstvibrating system 21 rotates about the rotation center axis X accordingto the first voltage V1. In other words, it is possible to prevent therotation of the driving member 211 about the rotation center axis Xaccording to the second voltage V2.

On the other hand, the magnetic field (this magnetic field is to becalled magnetic field B1) that tends to draw the area around the spacer81 of the driving member 211 toward the coil 62 by using the firstvoltage V1 and separate the area around the spacer 82 of the drivingmember 211 from the coil 62 and the magnetic field (this magnetic fieldis to be called magnetic field B2) that tends to separate the areaaround the spacer 81 of the driving member 211 from the coil 62 and drawthe area around the spacer 82 of the driving member 211 toward the coil62 are alternately switched.

In this case, seen in a plan view of FIG. 1, the spacer 81 is positionedon one side with respect to the rotation center axis Y of the drivingmember 211 and the spacer 82 on the other side. In other words, thespacers 81, 82 are arranged so as to sandwich the rotation center axis Yseen in a plan view of FIG. 1. Therefore, as the magnetic filed B1 andthe magnetic field B2 described above are switched alternately, thesecond axis members 222, 223 are deformed to be twisted while themovable plate 221 rotate together about the rotation center axis Y withthe frequency of the second voltage V2.

Note that the frequency of the second voltage V2 is same as thetorsional resonance frequency of the second vibrating system 22.Therefore, it is possible to let the movable plate 221 rotate about therotation center axis Y dominantly with the second voltage V2. In otherwords, it is possible to prevent the rotation of the movable plate 221about the rotation center axis Y according to the first voltage V1.

As described above, in the actuator 1, by applying the voltage resultingfrom superimposition of the first voltage V1 and the second voltage V2to the coil 62, the movable plate 221 can rotate about the rotationcenter axis X with the frequency of the first voltage V1 and also aboutthe rotation center axis Y with the frequency of the second voltage V2.By this, low cost and miniaturization can be achieved while the movableplate 221 can rotate about both of the rotation center axis X and therotation center axis Y.

In particular, the respective numbers of permanent magnet and the coil,which are driving source, can be reduced, so simple and smallconstruction can be obtained.

Further, by adequately changing the first voltage V1 and the secondvoltage V2, desired vibrating properties can be obtained withoutchanging design of the base body 2 or the permanent magnet 61.

Furthermore, the actuator 1 is constructed such that the permanentmagnet 61 is provided on the driving member 211 and the coil 62 isprovided on the opposite substrate 5 so as to oppose the permanentmagnet 61. In other words, the coil 62, which is a heating body, is notprovided on the first vibrating system 21. As a result, thermalexpansion of the base body 2 due to heat generated from the coil 62 atthe time of energization can be suppressed. Accordingly, the actuator 1can exhibit desired vibrating properties even when it used continuouslyfor many hours.

Such the actuator 1 can be fabricated as follows, for example.

FIG. 5A through FIG. 5H are views for illustrating a method formanufacturing the actuator 1 (corresponding to a longitudinal sectionalview taken along with the line A-A of FIG. 1). Note that for the sake ofconvenience of explanation hereinafter the upper side of FIGS. 5Athrough 5H is called upper side and the bottom side bottom side.

As shown in FIG. 5A, a SOI substrate 100 to be used for forming the basebody 2 and the spacers 81, 82 is prepared. Such the SOI substrate 100has a laminated structure, in which a Si layer 100 a, SiO₂ layer 100 band a Si layer 100 c are stacked. Then, as shown in FIG. 5B, formed onthe upper surface of the Si layer 100 a is a resist mask M1 that has ashape corresponding to shapes seen in plan view of the movable plate221, the second axis members 222, 223, the driving member 211, the firstaxis members 212, 213 and the supporting portion 23. Formed on thebottom surface of the Si layer 100 c is a resist mask M2 that has shapecorresponding to shapes seen in plan view of the spacers 81, 82.

After that, the Si layer 100 a is subjected to etching via the resistmask M1. Then, the resist mask M1 is removed. As a result, the Si layer100 a having the movable plate 221, the second axis members 222, 223,the driving member 211, the first axis member 213, the supporting member23 formed integrally, as shown in FIG. 5C. Note that the SiO₂ layer 100b functions at this time as a stop layer for etching. As such theetching method, for example, physical etching technique such as plasmaetching, reactive ion etching, beam etching or light assist etching,chemical etching technique such as wet etching or the combination of twoor more of those techniques can be used. It should be noted that thesame technique can be used for the etching in the steps described later.

After that, the Si layer 100 c is subjected to etching via the resistmask M2. Then, the resist mask M2 is removed. As a result, the Si layer100 c having the tip portion 812 of the spacer 81 and the tip portion822 of the spacer 82 formed, as shown in FIG. 5D. In this case, the SiO₂layer 100 b functions as a stop layer for etching.

Then, SiO₂ layer 100 b is removed except the area corresponding to theshapes seen in a plan view of the spacers 81, 82 so that the SiO₂ layer100 b having the base portion 811 of the spacer 81 and the base portion821 of the spacer 82 formed can be obtained. In other words, the spacers81, 82 integrally formed on the driving member 211 can be obtained. Asthus the SOI substrate is used, it becomes possible to integrally formthe spacers 81, 82 and the driving member 211 very easily.

After that, as shown in FIG. 5F, formed on the upper surface of themovable plate 221 is a metal film, thereby forming a light reflectingportion 221 a. As such the forming technique of the metal film, thereare known, for example, dry plating technique such as vacuum deposition,sputtering (low-temperature sputtering) or ion plating, wet platingtechnique such as electrolytic plating or electroless deposition,thermal spraying, bonding of metal layers or the like.

Then, as shown in FIG. 5G, the hard magnetic material havinglongitudinal shape on the bottom surface of the spacers 81, 82 is bondedto the driving member 211. Then, by energizing the hard magneticmaterial, the permanent magnet 61 can be obtained. As a result, thespacer 81, 82 are sandwiched between the driving member 211 and thepermanent magnet 61, thereby forming the space 83.

On the other hand, the supporting substrate 3 and the opposite substrate5 are formed by performing etching to the silicon substrate (not shown).The fabrication technique of such the supporting substrate 3 and theopposite substrate 5 is similar to the fabrication technique of the basebody 2 etc. from the SOI substrate 100 and the explanation therefore isomitted. Note that the coil 62 is fixed on the upper surface of theopposite substrate 5.

Finally, the base body 2, the SOI substrate 100 having the spacers 81,82 integrally formed, the supporting substrate 3 and the oppositesubstrate 5 are bonded to each other, thereby achieving the actuator 1,as shown in FIG. 5G. The bonding technique is not limited. For example,it is possible to perform bonding by using adhesive or by anodicbonding.

The actuator 1 described above includes the light reflecting portion 221a. Therefore, the actuator 1 can be preferably utilized for an opticalscanner included in a laser printer, a barcode reader, a confocalscanning laser microscope, an imaging display. It should be noted thatthe optical scanner according to the invention has the same constructionas the above-mentioned actuator and is therefore not explained here.

With reference to FIG. 6, the case in which the actuator 1 is used as anoptical scanner for an imaging display, as an example of an imageforming apparatus. Note that the longitudinal direction of a screen S iscalled lateral direction and the direction perpendicular to thelongitudinal direction is called lengthwise direction. Further, therotation center axis X is parallel to the lateral direction of thescreen S and the rotation center axis Y is parallel to the lengthwisedirection of the screen S.

An image forming apparatus (projector) 9 has a light source device 91for emitting light such as laser, a plurality of dichroic mirrors 92,92, 92 and the actuator 1.

The light source device 91 includes a red light source device 911 foremitting red light, a blue light source device 912 for emitting bluelight and a green light source device 913 for emitting green light.

Each of the dichroic mirrors is an optical element that synthesizes therespective lights emitted from the red light source device 911, the bluelight source device 912 and the green light source device 913.

Such the projector 9 synthesizes the lights emitted from the lightsource device 91 (the red light source device 911, the blue light sourcedevice 912, the green light source device 913) at the dichroic mirrors92. The resulting synthesized light is subjected to two-dimensionalscanning of the actuator 1, resulting in a color image formed on thescreen S.

At the time of two-dimensional scanning, as the movable plate 221 of theactuator 1 rotates about the rotation center axis Y, the light reflectedat the light reflecting portion 221 a is scanned in the lateraldirection of the screen S (main scanning). On the other hand, as themovable plate 221 of the actuator 1 rotates about the rotation centeraxis X, the light reflected at the light reflecting portion 221 a isscanned in the lengthwise direction of the screen S (sub-scanning).

As shown in FIG. 5A through FIG. 5H, the light synthesized at thedichroic mirrors 92 is subjected to two-dimensional scanning of theactuator 1 and then reflected at a fixed mirror K, thereby forming animage on the screen S. However, it should not be construedrestrictively. The fixed mirror K can be omitted and the light subjectedto two-dimensional scanning of the actuator 1 can be directly emitted onthe screen S.

As described above, the actuator, the optical scanner and the imageforming apparatus have been explained with reference to the embodimentsshown in the drawings. The present invention is, however, not limitedthereto. In the case of the actuator, the optical scanner and the imageforming apparatus according to the invention, the respective componentscan be substituted by any elements having similar functions or anyelements may be superimposed.

Further, according to the embodiment describes above, the actuator has asymmetrical shape with respect to the rotation center axis X and therotation center axis Y. However, the actuator may have an asymmetricalshape.

Furthermore, according to the embodiment described above, the permanentmagnet has a longitudinal shape. However, the shape of the permanentmagnet is not limited as long as the permanent magnet is provided suchthat a line segment connecting the both poles of the permanent magnetinclines with respect to the rotation center axis X and the rotationcenter axis Y, seen in a plan view of the movable plate. For example,the shape of the permanent magnet may be, seen in a plan view of themovable plate, a ring or a square. For instance, a pair of yokes may beprovided so as to hold in the direction of the line segment connectingthe both poles of the permanent magnet and magnetic flux may beconducted by those yokes.

1. An actuator, comprising: a first vibrating system having a frame-likedriving member and a pair of first axis members holding the drivingmember so that the driving member is rotatable about an X axis; a secondvibrating system having a movable plate provided inside the frame of thedriving member and a pair of second axis members holding the movableplate on the driving members so that the movable plate is rotatableabout a Y axis orthogonal to the X axis; a driving unit including apermanent magnet of longitudinal shape provided on the driving member, acoil provided to oppose the permanent magnet and a voltage applying unitapplying voltage to the coil; and a spacer sandwiched between thedriving member and the permanent magnet so as to form space between thepermanent magnet and the movable plate, the permanent magnet beingprovided such that the longitudinal line of the permanent magnetinclines, in a plan view of the movable plate, with respect to the Xaxis and the Y axis, and the voltage applying unit applying voltage tothe coil so that the movable plate rotates both about the X axis andabout the Y axis.
 2. The actuator according to claim 1, the spacer isintegrally formed with the driving member.
 3. The actuator according toclaim 2, the driving member being formed from one of a Si layer of a SOI(silicon on insulator) substrate, and the spacer being formed from atleast a SiO₂ layer, the SOI substrate having the SiO₂ layer, the one Silayer and the other Si layer.
 4. The actuator according to claim 1, thespacer being provided as one pair.
 5. The actuator according to claim 1,the frequency of the second voltage being the same as a resonancefrequency of the second vibrating system, the frequency of the firstvoltage being different from a resonance frequency of the firstvibrating system.
 6. The actuator according to claim 1, the frequency ofthe second voltage being larger than the frequency of the first voltage.7. The actuator according to claim 1, the permanent magnet having alongitudinal shape and being provided along a line segment passingthrough an intersecting point of the X axis and the Y axis and incliningwith respect to one of the X axis and the Y axis at an angle of 30° to60°.
 8. The actuator according to claim 1, the coil being provideddirectly under the permanent magnet.
 9. The actuator according to claim1, the coil being, in a plan view of the movable plate, formed so as tosurround outer periphery of the driving member.
 10. The actuatoraccording to claim 1, the movable plate including a light reflectingportion having light reflective properties on one surface thereofopposite from the other surface adjacent to the permanent magnet.
 11. Anoptical scanner, comprising: a first vibrating system having aframe-like driving member and a pair of first axis members holding thedriving member so that the driving member is rotatable about an X axis;a second vibrating system having a movable plate wherein a lightreflecting portion is formed provided inside the frame of the drivingmember and a pair of second axis members holding the movable plate onthe driving members so that the movable plate is rotatable about a Yaxis orthogonal to the X axis; a driving unit including a permanentmagnet of longitudinal shape provided on the driving member, a coilprovided to oppose the permanent magnet and a voltage applying unitapplying voltage to the coil; and a spacer sandwiched between thedriving member and the permanent magnet so as to form space between thepermanent magnet and the movable plate, the permanent magnet beingprovided such that the longitudinal line of the permanent magnetinclines, in a plan view of the movable plate, with respect to the Xaxis and the Y axis, and the voltage applying unit applying voltage tothe coil so that the movable plate rotates both of about the X axis andabout the Y axis so as to perform a two-dimensional scanning of lightreflected at the light reflecting portion.
 12. An image formingapparatus comprising an optical scanner including: a first vibratingsystem having a frame-like driving member and a pair of first axismembers holding the driving member so that the driving member isrotatable about an X axis; a second vibrating system having a movableplate wherein a light reflecting portion is formed provided inside theframe of the driving member and a pair of second axis members holdingthe movable plate on the driving members so that the movable plate isrotatable about a Y axis orthogonal to the X axis; a driving unitincluding a permanent magnet of longitudinal shape provided on thedriving member, a coil provided to oppose the permanent magnet and avoltage applying unit applying voltage to the coil; and a spacersandwiched between the driving member and the permanent magnet so as toform space preventing intervention by the movable plate, the permanentmagnet being provided such that the longitudinal line of the permanentmagnet inclines, in a plan view of the movable plate, with respect tothe X axis and the Y axis, and the voltage applying unit applyingvoltage to the coil so that the movable plate rotates both of about theX axis and about the Y axis so as to perform a two-dimensional scanningof light reflected at the light reflecting portion.